[Validation study of analysis of Malachite green in broiled eels (Kabayaki) by LC-MS/MS].

An improved method for analysis of Malachite green (MG) and its metabolite, Leucomalachite green (LMG), in broiled eels without using dichloromethane was developed. This method was evaluated by means of recovery tests according to the guideline for validation of analytical methods by the Ministry of Health, Labour and Welfare of Japan. MG and LMG were extracted from spiked samples with acetonitrile and citric acid/disodium hydrogen phosphate buffer solution, and were salted-out with sodium chloride. The acetonitrile layer was dried over anhydrous sodium sulfate and purified on C18 and strongly acidic cation exchange columns. MG and LMG in the purified solution were determined quantitatively using LC-MS/MS by the internal standard method with surrogates, MG and LMG labeled with deuterium (MG-d5, LMG-d6). The recovery rates of MG and LMG were 99.2% and 93.6%, respectively. The relative standard deviations of repeatability were 2.2% for MG and 4.4% for LMG, and the relative standard deviations of within-laboratory reproducibility were 3.5% for MG and 5.1% for LMG.